Minimizing power consumption is critical in extending operating time in portable or battery power devices. The lower the power consumption of the circuit elements of, for example, a handheld cell phone, the longer the handheld cell phone can provide its functionality to the user. Accordingly, circuit elements of a given device are designed for minimal power consumption.
Low power consumption constraints generally apply to all elements of an integrated circuit device, such as, for example, processors, output drivers, displays, etc. The circuit elements are designed to interact and function with each other, and must adequately perform their required function while remaining within the desired power consumption constraints. Oscillator circuits comprise one of the most fundamental circuit elements of electronic devices.
Oscillators are used to produce a wide variety of periodic signals (e.g., clock signals, etc.). Many of the components of an integrated circuit device rely on clock signals generated by oscillator circuits to produce their functionality. For example, modern analog to digital converters (ADCs) function by using low jitter external clock source. ADCs are specified to operate with a clock signal having a duty cycle that varies across a specified range.
Similarly, most signal sampling mechanisms common to data communication applications rely on high-quality clock signals to sample incoming data. It is becoming increasingly common for such sampling mechanisms to function on both the rising edge and the falling edge of a clock signal, thereby making duty cycle control an important factor. As is well known, a clock signal's duty cycle refers to a ratio of one clock phase width to the entire clock period.
A problem exists, however, with prior art oscillator circuits. As described above, high-quality clock signals are critical to functioning of many different functional blocks of an integrated circuit device. To produce such high-quality clock signals, and to provide a precise adjustable duty cycle, prior art oscillator circuits include a large number of transistors, current sources, and other circuit elements. These elements tend to increase power consumption, thereby reducing battery life of a handheld device. Additionally, a large number of circuit elements increase the amount of silicon area dedicated to the oscillator circuit, thereby increasing the cost of the overall device.
Prior art FIG. 1 shows a diagram of a typical prior art oscillator circuit 100. The prior art oscillator circuit 100 includes two amplifiers 151-152. The oscillation is driven primarily from the action of the amplifiers 151-152, which function as comparators. The output of the comparators 151-152 are respectively coupled to the NAND gates 121-122 as shown. The NAND gates 121-122 are coupled in a feedback loop as depicted, which oscillates between a high-value and a low value. The output of the oscillator circuit 100 is derived from the output of the inverter 123.
The oscillator circuit 100 includes the current sources 101-105 as shown. The high voltage level and the low voltage level between which the oscillator circuit 100 oscillates is set by the voltages V1 and V2 as derived from the current from the current source 101 flowing through a resistor 111 and a resistor 112. The voltages V1 and V2 are coupled to the positive input of comparator 151 and the negative input of comparator 152 as shown. In this manner, the current source 101 (e.g., I1) creates the voltages V1 and V2.
The current source 102 and the current source 103 bias the comparators 151-152 as shown. The current source 104 and the current source 105 are used to charge and discharge the capacitor C1, and thereby produce the output signal at node 130. As shown in prior art FIG. 1, the current source 104 charges the capacitor C1 to the voltage V2 and the current source 105 discharges the capacitor C1 to the voltage V1.
One problem with prior art oscillator circuit 100 is that it consumes too much power. As shown in prior art FIG. 1, the oscillator circuit 100 requires five current sources 101-105 in order to function. Each of these current sources represents a power consuming element. Another problem is the fact that the prior art oscillator circuit 100 requires two comparators 151-152, which both consume power.
Yet another problem with the prior art oscillator circuit 100 is the fact that it requires a constant current flow, and thus a constant power drain, from the current source 101 across the resistor 111 and the resistor 112. These current flows are required in order to create voltages V1 and V2.
Thus, what is required is a solution for implementing a very low power consumption oscillator circuit for an integrated circuit device. The required solution should provide an adjustable duty cycle that can be set in accordance with the needs of a given application. Additionally, the required solution should require fewer circuit elements in comparison to prior art oscillator circuit implementations.